The new Chip Scale Package LED (CSP LED) based on flip chip is a LED that packages the packaging glue onto the top surface and side surfaces of chips on the bottom surface of which electrode are arranged, so that the electrode could be exposed. The packaging cost can be reduced by this packaging structure without bracket or substrate. In general, five light-emitting surfaces are utilized in existing CSP LEDs, that is, light can be emitted from the top surface and four side surfaces of a LED, and the packaging process of this kind of LED is relatively simple. With the improvement of people's demand for angle and consistency of light emitted, the structure of existing CSP LEDs can't meet the demand of people, the emergence of a CSP LED with a single light-emitting surface is desired. A packaging structure of CSP LED disclosed in Chinese Patent No. CN104112810A comprising a LED chip and packaging glue packaged on the top surface and side surfaces of the LED chip, an electrode is arranged on the bottom surface of the LED chip, a reflector is arranged on at least one of the following parts of the packaging glue: bottom surface and side surfaces. The reflector is a reflecting surface or reflecting plane extending from the bottom surface of the self-packaging glue to side surfaces. Light extraction efficiency could be improved and angle of light emitted by spraying a reflecting layer on the bottom surface and side surfaces of the self-packaging colloid, and a single light-emitting surface can be formed. Although a single light-emitting surface can be achieved for a product by this approach, packaging process is complicated. Since the reflector for blocking light is formed through spraying, for such process only could be performed on a single LED, efforts and resources consumed by this process would be undoubtedly enormous, which causes it's not suitable for large-scale production.
Covering fluorescent glue onto the surface of a LED chip is the main process in the packaging process of CSP LED; however, a fluorescent glue layer is usually formed by molding or printing in existing fluorescent glue covering process. The low LED production efficiency is mainly because the complicated fluorescent glue forming processes.
Existing making process of single CSP without a substrate is that: first, laying film on a machine, then placing multiple chips on the film followed by packaging the fluorescent glue on the film, and solidifying the fluorescent glue to coat chips except the bottom surface with the fluorescent glue, cutting the chip groups formed into single CSPs.
During cutting, there may be some downward burrs formed on the lower edge of the fluorescent glue layer which causes rugged phenomenon between the fluorescent layer and the bottom of the chips. When the CSP is packaged on a flat substrate, the existence of the burrs makes it difficult for the chips to closely contact with the substrate, thus the reliability of the electrical connection may be affected.
Currently, the connection between the CSPs and the substrate is achieved by placing solder paste and flux onto the substrate, and then applying solder reflow. The plane on which the fluorescent glue layer and the bottom surface of the chips are may be rugged due to the expansion of the fluorescent glue layer during heating, this will result in the occurrence of loose contact, void contact of even no contact when the chips are bonded to the pads on the substrate, the reliability of the electrical connection between the chips and the substrate may be affected.
In view of the technical problems mentioned above, a special structure of flip chip is applied by the inventor. The inventor believes that if the flip chip electrode and the packaging glue form a step, these technical problems may be solved by forming a step with electrode of the flip chip and fluorescent glue. However, it's difficult to form a step between the electrode and fluorescent glue during packaging, because the fluorescent glue is fluid before solidification in fabricating CSP chip. This creates a bottleneck in fabricating.
For side-emitting light source module such as panel light, backlight module and so on, usually light emitting device such as a light bar is fixed on the side of the side-emitting light source module by a lamp, so that light usually emitted from side surface and exported by some optical device.
In view of the light source module mentioned above, existing ordinary light emitting devices are mainly used at present, for example a light emitting device composed of a chip and fluorescent glue, a light emitting device composed of a chip, a bracket, and fluorescent glue. In general, there should be multiple light emitting devices placed on the substrate to form a light source. As shown in FIG. 22, for a light emitting device 100a composed of a chip and fluorescent glue, the chip may usually have light emitting angle of its own, there will be a dark area 300a between two light emitting devices after the light emitting device 100a is mounted on the substrate 300, since the light emitting angle of the chip is relatively small, there may be a dark area 300a between tow light emitting devices which might influence the consistency of light emitted. Also, the light bar is fixed to the side surface of the light source by a clamp, there may be a certain degree of blocking caused by the clamp to the light emitting device, so light emitted from part of the light emitting device corresponding to the clamp may be wasted. In addition, the light emitting device emits light to all around, but only light along the direction of the length of the substrate and light from the top surface could be used, the rest could not be used well, which causes a lower light utilization.
Similarly, there will be problems mentioned above as well if a light emitting device composed of a chip, a bracket, and fluorescent glue is used.
Nowadays, CSP packaging structure is widely used in various fields because of its small size, light weight and good electrical performance.
Current CSP packaging structure mainly includes a flip chip and packaging glue packaged on the flip chip, the packaging glue is fluorescent glue. Light can be emitted from each surface of the flip chip, if the CSP packaging structure is mounted on a substrate, light can be emitted from each surface except for the bottom surface. However, for a special light source, light emitted from some side surfaces couldn't be used, result in low light utilization.